Acne vulgaris (or simply acne) is a common human skin disease, characterized by presence of comedones (blackheads and whiteheads), papules (small pinkish 5 mm or smaller bumps), pustules (pus filled papules), nodules (large painful lesions located in the deeper portions of the skin), and in more severe forms, cystic abscess-like fluctuant lesions. Papules, pustules, nodules, and cystic type lesions, can all lead to secondary scarring. Severe inflammatory can manifest clinically by presence of not only comedones, but also by papules, pustules, nodules, and cystic lesions (with the cystic lesions representing the most severe manifestation of acne). Alternatively, in milder cases, acne can manifest clinically in non-inflammatory lesions such as open and closed comedones. It is important to realize, however, that even comedones have microscopically and histologically been shown to be accompanied by varying degrees of inflammation.
Acne more often affects skin with a greater numbers of oil glands; these areas include the face, the upper part of the chest, and the back. In adolescence, acne is usually caused by an increase in androgens such as testosterone, which occurs during puberty, regardless of sex. The psychosocial impact of acne has been well documented. Body image issues associated with acne can result in depression, anxiety, social isolation, low self-esteem, and even suicide.
Many different treatments have been proposed for decreasing acne. Some treatments involve dietary changes, such as eating fewer simple carbohydrates like sugar. Medications for acne include: benzoyl peroxide, antibiotics (either topical or by pill), retinoids (topical or oral) as with Isotretinoin (more commonly known as Accutane®), sulfur based medications, anti-androgen medications, hormonal treatments such as birth control pills, and alpha and beta hydroxyl acids (salicylic acid). Early and aggressive treatment is advocated by some to lessen the overall long-term impact to individuals.
The pathogenesis of acne, considered primarily to be a disease of the pilosebaceous unit, is attributed to multiple factors such as increased sebum production, alterations of the quality of sebum lipids, inflammatory processes, dysregulation of the hormone microenvironment, and interaction with neuropeptides, follicular hyperkeratinization and the proliferation of pathogenic bacteria within the follicle. In particular, the sebaceous gland plays an important role in the initiation of the disease, as this gland possesses all the enzyme machinery for the production of hormones and cytokines.
The pathogenic bacteria involved in acne is the Propionibacterium acnes (P. acnes), a gram positive anaerobic bacteria that grows deep inside of pores, where it feeds on the sebum that is produced by the sebaceous glands that surround the base of the hair shaft. P. acnes bacteria use sebum, which is produced in follicles, as a primary source of food. P. acnes bacteria use specialized enzymes that digest the fatty acids and triglycerides that are abundant in sebum. In an anaerobic environment, P. acnes ferments the fatty acids and triglycerides, and releases short chain fatty acids and propionic acid as metabolic byproducts (hence, the name Propionibacterium). The cellular damage, metabolic byproducts and bacterial debris produced by the rapid growth of P. acnes in follicles can trigger secondary inflammation, which is a contributing factor to the severity of acne symptoms.
Among the factors implicated in acne occurrence, sebum secretion can be considered as the major one. Increased sebum secretion is a characteristic of acne patients. Along with the increased sebum secretion, several qualitative modifications have been described in acne patients, underlying the pivotal role played by lipid mediators derived from sebum alterations in acne pathogenesis. Human sebum contains triglycerides, wax esters, squalene, cholesterol esters, cholesterol, and free fatty acids. Triglycerides and fatty acids, taken together, account for the predominant proportion (about 57.5%), followed by wax esters (about 26%) and squalene (about 12%). Abnormal activity of specific desaturase enzymes and/or excessive sebum secretion can result in an alteration of the relative proportion of the different fatty acids, and leading to compositional changes that can initiate and exacerbate acne symptoms. This accounts for modifications in the amount, and type of fatty acids which have been observed in acne patients. Specifically and importantly squalene peroxide, a by-product of lipid peroxidation derived from sebum, has been recognized to play a crucial role in the development of inflammatory reactions as well as in cytotoxicity and comedogenesis.